A variety of medical electrode leads are available today for the diagnosis and treatment of various disorders of the cardiovascular and neurological systems. These electrode leads can be used to sense electrical activity within the body and to deliver different forms of energy to stimulate, ablate, cauterize or pace. The core electrode technology common to all of these lead designs is the application of one or more metallic bands on a lead body. Examples of medical leads using metallic banded electrodes include permanent and temporary cardiac pacing leads, electro-physiologic (EP) leads, electrocautery probes and spinal stimulation leads. The use of pre-formed metallic band electrodes manufactured from noble metals, such as gold or platinum and various other conductive alloys has found widespread application despite their functional design and performance limitations.
Metallic band electrodes possess distinct steerability problems. The steerability problems arise from the inflexible nature of the circular rings or bands. These inflexible bands of metal are typically adhesively bonded, crimped or otherwise attached to the exterior surface of the lead body. The bands are electrically coupled to electrical conductors that typically extend through one or more lumens in the lead body. The bands tend to be relatively thick and are therefore rigid. For neurological applications, the bands are typically about 3 millimeters wide. When it is considered that often multiple ring electrodes are employed at spaced locations along the distal end portion of the lead body, they significantly impact the ability of the distal end portion of the lead to flex and conform to tissue structures.
As noted above, band electrodes placed on a flexible lead stiffen the lead and thereby reduce its steerability. As such, leads having band electrodes are often restricted to applications where steerability and selective placement are not required and affect a variety of applications.
In cardiac therapies, such as for example ablation therapy, precise steerability and placement of a lead is necessary. Ablation therapy requires that a lead having sensing/ablation electrodes on the distal end is steered through the patient's vascular system and into a predetermined chamber of the heart. The lead is manipulated so as to place the electrodes into direct contact with the myocardial tissue that is sensed and/or to be ablated. The aberrant path and/or ectopic foci is first located using a mapping technique in which cardiac depolarization signals picked up by the electrodes are transmitted over electrical conductors in the lead to a suitable monitor/analyzer. Once located, the aberrant conductive pathway or the ectopic foci is ablated. This procedure requires the ability to precisely control the lead over the surfaces of the heart. Therefore, a need exists for a lead that provides precise control and steerability to accurately locate the electrodes in the heart.
The process of terminating an arrhythmia such as ventricular fibrillation is accomplished by means of a high energy shock to the myocardium. When using defibrillation leads placed inside the heart (endocardially), the most accepted method to deliver the shock is through a helical wound coil electrodes placed inside the heart.
The method of using helical wound coils to terminating atrial or ventricular fibrillation is satisfactory in principle. Coils do however have large gaps and spaces between the windings which encourage fibrotic growth to intertwine. This effectively locks the lead into the myocardial tissue. The lead then becomes extremely difficult if not impossible to remove without invasive surgery. Furthermore, coil electrodes can stretch, unwind, expand, or contract. This can give the implanting physician an unreliable sense of feel when implanting the lead. The lead can also build up a torque load (similar to winding up a spring) if the lead is twist or turned.
Another disadvantage to coil windings is that the coils are positioned on the outer lead body. This increases the overall diameter of the lead significantly. Furthermore, the coil windings result in a stiffer lead since the coils restrict the bending of the lead.
There is a problem regarding low voltage bradycardia ring electrodes. Traditionally, ring electrodes for low voltage applications use a solid tube (or ring) for creating the electrode. Historically, this design has been utilized for all low voltage applications. However, it can become difficult when placing LV leads with ring electrodes in the left side of the heart via the coronary sinus. The ring electrodes are a hindrance because of the stiffness they incur on the lead. Since the ring is a solid tube of metal, the lead stiffens in the region of the ring. This stiffness makes the lead very difficult if not impossible to place in the left side of the heart through the coronary sinus.
Also, an RV or RA ring electrode can hinder placement of a lead by creating a stiff section which can create drag or jamming in an introducer sheath or within the vein when implanting the lead.
A number of patents typify the prior art in regard to lead constructions for cardiac pacing, for example, intended to be placed in the chambers of the heart or the coronary venous system and thereby subjected to a series of tortuous bends, the leads having the flexibility to follow these bends but having enough structural support to allow them to be pushed and twisted in order to navigate within these veins.
In this regard, U.S. Pat. No. 4,280,511 to O'Neill discloses a ring electrode for a pacing lead in which the electrode is secured to a conductor coil by soft metal disposed in a slit in insulation covering the conductor coil. U.S. Pat. No. 5,458,629 to Baudino et al. discloses a lead in which ring electrodes are constructed according to a novel technique in which the body of the lead is etched or milled to provide notches and the ring electrodes are formed by enplacing a C-shaped conductor over the notch and closing it into place to provide an isodiametric lead construction. U.S. Pat. No. 6,493,590 to Wessman et al. discloses a lead construction provided for use in stimulating body tissue or an organ that has a flexible band electrode including at least one slot configured to provide increased flexibility.